1. Field of the Invention
The present invention relates to a stabilized isothiazolone formulation. More specifically, it relates to a highly stabilized liquid formulation containing an isothiazolin-3-one compound useful as a non-medicinal biocide, which is capable of inhibiting decomposition of the isothiazolin-3-one compound even stored for a long period of time at room temperature or above.
2. Description of the Prior Art
Isothiazolone compounds such as 5-chloro-2-methylisothiazolin-3-one and 2-methy-isothiazolin-3-one have so far been known as a non-medicinal blocidal, antiseptic or antifungal agents. They are, in particular, useful as antiseptic or antifungal agents for synthetic polymeric emulsions such as NBR latex, SBR latex and acrylic resin emulsion.
The isothiazolone compounds are highly water-soluble, and accordingly it is desired to use them in the form of an aqueous solution in view of their dispersion into systems to be treated. However, the active ingredient of the aqueous isothiazolone formulations is decomposed in a short period of time to result in a precipitate, and at the same time, the content of an isothiazolone compound in the formulation decreases. Therefore, a mere aqueous solution of the compound is extremely unstable as a formulation, and cannot be put into practical use at all.
In view of the above, there has been proposed an aqueous formulation imparted with stability by forming an isothiazolone compound as a complex with a metal salt, such as a calcium or magnesium salt, or further adding thereto a stabilizer such as magnesium nitrate, and then dissolving it in water or in an aqueous solvent (Japanese Patent Laid-Open No. 23968/1979, U.S. Pat. No. 3,870,795). There has also been proposed recently an organic solvent formulation not containing water nor a metal salt, or a remarkably reduced amount of the same, which is prepared by dissolving an isothiazolone compound in a particular organic solvent, such as glycol-type solvent (Japanese Unexamined Patent Publication Nos. 56174/1986, 212576/1986).
Further, Japanese Unexamined Patent Publication No. 85271/1990 suggests the dissolving of an isothiazolone compound in a single or mixed solvent of two or more solvents selected from the group of ethylene glycol monomethyl ether acetate, ethylene glycol dimethyl ether, propylene carbonate, dimethylformamide, and the like; however this document specifically discloses the stability of formulations each containing a single solvent of the above solvents in which an isothiazolone compound is dissolved.
However, if the conventional aqueous formulation containing a complex of isothiazolone compound with a metal salt or containing a metal salt stabilizer as described above is added as it is by an effective amount as an antiseptic or antifungal agent to a synthetic polymeric emulsion, there arises a problem that the emulsion phase is broken to cause phase separation or coagulation (so-called emulsion shock) due to the effect of polyvalent metal ions such as of calcium or magnesium ions contained in the formulation, resulting in decreased antiseptic or antifungal action of the isothiazolone compound.
Further, although the above organic solvent formulation does not cause emulsion shock, it cannot contain an isothiazolone compound at high concentration. In addition, the decomposition of the isothiazolin-3-one compound cannot be satisfactorily inhibited when the formulation is stored for a long period of time. For example, the above U.S. Pat. No. 3,870,795 teaches at column 4, lines 35-45 that a non-aqueous solution containing about 25% of 5-chloro-2-methyl-3-isothiazolone/2-methyl-3-isothiazolone (93:7) decomposed completely when allowed to stand at 50.degree. C. for 28 days.
The present invention has been made in view of the foregoing situations, and it is an object thereof to provide an isothiazolone compound formulation, not containing the above polyvalent metal ions, which is excellent in long storage stability.